The invention relates generally to turbomachinery, and more particularly, to inlet assembly construction for use in a low pressure section of a steam turbine.
A low pressure (LP) inlet in a steam turbine casing is designed to transfer working fluid, i.e. steam, from the power plant piping to an LP turbine section, where it causes the rotor to rotate. An inlet assembly can guide the flow to an inlet bowl, which can further redirect the flow, such as by turning it through an angle to be received by the rotor. Typically, the inlet bowl will be connected to the inlet assembly along an edge of the inlet bowl. The inlet assembly can shape and direct the flow from the circular cross section pipe to the polygonal or substantially polygonal exit geometry to minimize losses through the transition. Such losses may be caused by discontinuities and flow obstructions in the inlet passage surfaces.
Inlet assemblies have been manufactured using a cone as the base. Cone-based construction has several challenges. Cones may require significant handwork to transition from the circular geometry at the upstream end to the polygonal or substantially polygonal geometry of the downstream end. Cones are also particularly costly geometric shapes to fabricate, requiring rolling in two dimensions, and generating excess waste. Additionally, cone-based inlet assemblies may only achieve substantially polygonal exit geometry, having curved edges on two sides of the downstream end. This may add complexity to affixing the inlet assembly to the edge of the inlet bowl.